When I'm driving over a washboard road at a certain low speed, I can hear a low frequency thumping/thud sound from the back. When I pound on the spare tire I think I hear the same sound. Everything is tight (wheel and spare tire mount), but when I hold the top of the back door(I can feel it vibrating when I hit the tire) and hit the tire the thumping sound is reduced. Anyone else notice this?

 

Is it possible it's the jack on the inside of the door?

 

My jack was loose and made that thumping noise..

 

I had a similar rattle. The dealer gave me a locking gas cap, and stuffed the old original gas cap in the storage compartment in the rear door where the jack is. After driving around and hearing a rattle whenever i went over bumps/rough road, I looked inside the door and found the gas cap! No more noise!

 

The jack was tight. I have to take off the spare and see if the thud goes away.